There are provided laser visualization devices which use laser beams to clearly visualize visualized objects located under water whose transparency is not good. The official gazette of Japanese Patent Laid-Open Publication No. Hei 7-072250, which is a patent gazette in Japan, and the like disclose the technology of such laser visualization devices.
Conventionally, this type of the laser visualization device is constructed by a laser oscillator which generates laser pulses (pulse-like laser beams), a light radiation detection device which radiates the laser pulses to a visualized object under water and which detects reflection light, and a control device which controls a direction of the light radiation detection device and which displays an image of the visualized object based on an output of the light radiation detection device. Among them, the laser oscillator and control device are equipped on a support ship on the sea, while the light radiation detection device is arranged and fixed in proximity to the visualized object under water.
In addition, this type of the laser visualization device is designed as follows:
Laser pulses generated by the laser oscillator equipped on the support ship are lead to the light radiation detection device, placed under water, via an optical fiber cable the laser pulses are radiated to the visualized object from the light radiation detection device, so that reflection light from the visualized object is detected by the light radiation detection device; and detection signals are transmitted to the control device on the support ship, so that an image of the visualized object is displayed on the monitor and the like.
Further, in the conventional laser visualization device, the light radiation detection device is provided inside of a pressure-proof vessel to provide resistance against water pressure and is supported by a pan-tilt device. In this case, the light radiation detection device has a relatively heavy weight, so it is necessary to use a relatively large size for the pan-tilt device. In the case where such a large size of the pan-tilt device is used, it is inconvenient to carry the light radiation detection device, so workability for the fixing work of the light radiation detection device under water is not good, while workability for the transfer of the device once fixed is not good as well.
On one hand, it is known that by improving the intensity of the laser pulses, a more clear image of the visualized object can be obtained. However, as described above, conventionally the laser pulses are transmitted and supplied to the light radiation detection device under water from the laser oscillator on the support ship via the optical fiber cable, so the intensity of the laser pulses which can be radiated to the visualized object is restricted by the light transmission capacity of the optical fiber cable. Therefore, it is not possible to obtain a sufficiently clear image of the visualized object, particularly in the case where the visibility distance becomes great, deterioration of the image is remarkable. Further, a YAG-OPO (Optical Parametric Oscillator) or else is used for the laser oscillator, so there is a problem that consumption of electric power is great.
Further, the light radiation detection device is constructed by a pan-tilt device which changes a radiation direction of laser pulses as well as a laser radiation unit and a laser receiving unit which are fixed on the pan-tilt device, wherein the pan-tilt device is fixed in proximity to the visualized object. Therefore, a range of the visualized object is limited by a mounting position of the light radiation detection device, while in the case where multiple visualized objects are subjected to visualization, it is necessary to change the mounting position of the light radiation detection device every time, which is not very handy. Changing of the mounting position of the light radiation detection device having a certain level of weight is very troublesome and is not good in workability.